DE-A 41 12 957 describes a solid bowl helix centrifuge somewhat similar to the solid bowl helix centrifuge whose principle features are indicated above. In the earlier-model, the rotor is delimited by face walls at both extremities and the decanting apertures in the wall of the cylindrical drum are very small; this has the effect of blocking the light phase that is to be decanted. The heavy phase is removed through narrow discharge apertures in the conical drum section. Since the face of the conical drum is closed, it is practically impossible to avoid clogging at this point. This in turn compromises the degree of purity of the light phase. The fact that the mixture to be separated enters the centrifuge in the front section of the cylindrical drum exacerbates this deficiency, since the heavy phase is deposited on the internal wall over the entire length of the rotor and must be transported from there by the scroll conveyor against the flow of the light phase. As a consequence, the scroll conveyor requires a relatively powerful motor.
A solid bowl helix centrifuge of the type disclosed herein is also shown and discussed in U.S. Pat. No. 5,792,039. Here too, the extremity wall of the conical drum is blind. In this case, the heavy phase that has entered the conical drum must be returned to the cylindrical drum axially of the scroll conveyor. To this end, the helices in the conical and the cylindrical drums are constructed to operate in opposing directions. The discharge ports for the heavy phase form a ring in the wall of the cylindrical drum and are arranged in such a way that they are axially offset toward the face wall of the cylindrical drum relative to the inlet apertures of the chamber in the hollow shaft. The effect of this configuration is that the heavy phase is moved in one direction within the conical drum and in the opposite direction in the cylindrical drum.
The disadvantages of the prior art are overcome by the present invention, and an improved solid bowl centrifuge is hereinafter disclosed which offers significant improvements over prior art centrifuges.